once xmms is running you can issue commands like "xmms --play" and "xmms --fwd" etc. (see man xmms). so all you would have to do is assign ctrl+a to run those commands. basically the same thing I had to do with my fancy media keyboard. except you have to bind regular key combinations where as I just used scancodes. I'm not familiar with fluxbox very well, but I think it uses something called bbkeys (correct me if I'm wrong) to bind key combinations to run specific commands.

yeah i know about bbkeys,, flux actually has its own built in.. the command is xmms -p for playing a song.. but the problem is that it launches a new xmms.. if i want to like pause, each time it will load up a new xmms...